The present invention involves a biorefinery process for pressure cooking woody or fibrous biomass (i.e., non-food plant biomass such as wood chips, plant stubble, food processing waste or other sources) in water to yield fermentable saccharides, commercial chemicals, and other useful lignocellulosic derivatives, and also to yield woody or fibrous solids that are significantly improved for manufacture of pulp and paper, fuel pellets, wood composites, bioconversion feedstock products such as crystalline cellulose, fermentable glucose, and other useful products.